I'm a Creative Cloud user at a Seattle non-profit. We've recently recevied source files for our corporate brochure. This brochure was developed in a Mac environment. We, the client, operate in a Windows environment.

If possible, I'd like to make a few minor changes to these files rather than employing another developer. After opening the InDesign document, I've worked through some of the dialog boxes, reconnecting assets that are found in the project subfolder. That all goes just fine.

But then we get to the fonts. First, I'm informed by a dialog box that there are missing fonts.

This is expected. However, then we get to this next dialog box where I note the substitutions:

And here is where I'm stuck in the mud.

Try as I might, I can't actually get the "Change" button to become an active choice. I have about half of the fonts noted here. I figure that Helvetica can become Arial, but am unable to actually activate it.

I searched TypeKit for Gotham, but could find nothing. Am I misremembering this as an Adobe Typekit font? I could have sworn it was. The little red "a" would seem to be a giveaway.

I think you and your deliverer should change the fonts to OTF and avoid T1 and TTF in the future. You need to buy licenses, more due to technical problems with T1 fonts. OTF are the same on Mac and Windows.